1. Field of the Invention
The present invention relates to an impact absorbing mechanism and a bumper reinforcement having the mechanism.
2. Description of the Related Art
As is well known, a vehicle such as an automobile is provided with an impact absorbing mechanism for absorbing an impact load when the impact load is applied to a vehicle body in, for example, a collision of the vehicle. In Japanese Patent Laid-open Publication No. 11-255049, for example, there is disclosed an impact absorbing structure for carrying out impact absorption by providing a crush box to a portion corresponding to a mounting portion where a reinforcement made of resin is mounted to a vehicle body. A reinforcing rib is provided to the reinforcement. Because the crush box is formed by partitioning an inside of a box body using a large number of ribs to create a so-called honeycomb-shaped structure, impact absorbing efficiency is satisfactory. However, as the impact absorbing structure is a whole structure, the impact absorption at the time of initial displacement is not satisfactory.
In Japanese Patent Laid-open Publication No. 10-76889, there is disclosed a structure in which a steel sheet is subjected to press forming to form a bumper reinforcement in a rectangular sectional shape separated vertically and extending longitudinally and brackets for mounting the bumper reinforcement to a vehicle body are provided to a curved side of the bumper reinforcement. In this prior art, by providing a substantially straight plate connecting the brackets, an impact absorbing effect is enhanced.
In recent years, providing both impact absorbing properties in two stages, i.e., properties of impact absorption in a displacement initial stage and absorption of a larger impact load after the initial stage are required of a bumper of an automobile. The former impact absorption (in the initial stage) corresponds to energy absorption for protecting a pedestrian on the chance that the automobile collides with the pedestrian, for example. The latter impact absorption corresponds to energy absorption for protecting a vehicle body on the chance that the vehicle collides with an object, for example.
However, in both the pieces of prior art, impact at the time of initial displacement is absorbed by bending of the reinforcement only and impact energy that can be absorbed by a narrow range of displacement is limited. Therefore, a satisfactory impact absorbing effect cannot be obtained in actuality. In other words, it is difficult to satisfactorily carry out impact absorption especially in the displacement initial stage by the prior-art bumper.
Furthermore, it is difficult to obtain an optimum impact absorbing structure such as a bumper based on a desk design and a structure having required properties is obtained by repeating field tests such as actual crash experiments and by trial and error. If specifications required for the impact absorbing structure such as a bumper are changed due to a change in design of a vehicle, for example, design and development to cope with the change can take considerable time and money.
The invention has been accomplished with the above various problems in view and it is a basic object of the invention to provide an impact absorbing mechanism by which impact energy absorbing performance in a displacement initial stage is enhanced to carry out efficient impact absorption and it is possible to relatively easily cope with changes in required impact absorbing properties. Also, it is another basic object of the invention to provide a bumper reinforcement in which the above mechanism is incorporated for carrying out impact absorption.
In order to achieve the above-mentioned objects, an impact absorbing mechanism according to a first aspect of the present invention is provided between receiving portions at a predetermined distance from each other for absorbing an impact load input between the receiving portions. This impact absorbing mechanism includes a dispersing transferring portion for dispersing and transferring the input impact load in a plurality of directions, impact absorbing portions for respectively absorbing dispersed impact loads from the dispersing transferring portion, and receiving stopping portions for respectively supporting the impact absorbing portions. The impact load is dispersed and absorbed in the plurality of directions by the impact absorbing mechanism.
With the impact absorbing mechanism according to the first aspect of the present invention, the impact load can be dispersed and transferred in the plurality of directions from the input initial stage (i.e., displacement initial stage) of the impact load, and the dispersed impact loads can be absorbed by the respective impact absorbing portions. Therefore, efficient impact absorption can be carried out from the displacement initial stage. Furthermore, if the impact absorbing properties required for the impact absorbing mechanism are changed, it is possible to cope with such changes relatively easily by changing design of the impact absorbing portions only.
Also, according to a second aspect of the present invention, there is provided a bumper reinforcement that includes a case body having a substantially angular U shape in section and an impact absorbing mechanism provided between receiving portions at a predetermined distance from each other for absorbing an impact load input between said receiving portions. This impact absorbing mechanism includes a dispersing transferring portion for dispersing and transferring said input impact load in a plurality of directions, impact absorbing portions for respectively absorbing dispersed impact loads from said dispersing transferring portion, and receiving stopping portions for respectively supporting said impact absorbing portions. The impact load is dispersed and absorbed in said plurality of directions by the impact absorbing mechanism. Furthermore, at least said dispersing transferring portion and said impact absorbing portions of said impact absorbing mechanism are housed in said case body. And, said impact load input side of said dispersing transferring portion is supported by upper and lower wall portions of said case body.
In the above aspects of the present invention, it is preferable that second impact absorbing portions for carrying out impact absorption after the impact load is transferred to the dispersing transferring portion are provided in portions corresponding to the receiving portions of the impact absorbing mechanism or in proximity of the portions.
By providing said second impact absorbing portions, the impact absorption can be carried out by the second impact absorbing portions after the impact load is transferred to the dispersing transferring portion. Therefore, it is possible to efficiently absorb the impact load with different absorbing properties in the initial stage and the middle stage after the initial stage.
In this case, it is more preferable that said receiving stopping portions are integrally formed with side faces of said second impact absorbing portions. Thereby, the structure of the receiving stopping portions and the second impact absorbing portions can be simplified.
Furthermore, in the above aspects of the present invention, it is preferable that the dispersing transferring portion is formed by connecting respective ends of a plurality of transferring members, and a connecting portion is positioned to be closer to load input sides than to the other end of the respective transferring members. Also, the impact absorbing members, for absorbing impact loads in directions along the transferring members, are disposed on the other ends of the respective transferring members.
By employing such a construction, the impact load can be reliably dispersed and transferred in the plurality of directions from the input initial stage of the impact load, and the dispersed impact loads can be respectively absorbed by the impact absorbing portions on the other ends of the respective transferring members, since the dispersing transferring portion is specifically formed by connecting the respective ends of the plurality of transferring members, and the connecting portion is positioned to be closer to the load input sides than to the other ends of the respective transferring members.
In this case, it is more preferable that the dispersing transferring portion includes two transferring members, the receiving stopping portions corresponding to the other ends of the transferring members being integrally connected to each other through a connecting member, and the connecting member and the two transferring members being respectively positioned on respective sides of a substantially triangular shape.
By employing such a constitution, the receiving stopping portions can be integrally connected to each other. Also, the substantially triangular structure can be formed by the connecting member and the two transferring members. And, it is possible to suppress outward movement of the receiving stopping portions that causes bending loads to act on support structures of the receiving stopping portions when the impact load is applied between the receiving stopping portions. Therefore, it is unnecessary to make the supporting structures of the receiving stopping portions excessively strong.
Furthermore, it is more preferable that a joint member substantially parallel to a straight line connecting the receiving portions is disposed as a connecting portion for connecting the respective ends of the transferring members. Thereby, impact load can be transferred along the respective transferring members through the joint member, and impact absorption can be carried out efficiently, even if the impact load is transferred to a portion that deviates from the center between the receiving portions.
Furthermore, it is more preferable that each of the impact absorbing members is formed into a box shape with ribs formed on an inside of the box shape. Thereby, it is possible to relatively easily adjust and change the impact absorbing property of the impact absorbing members by changing design features such as shapes and plate thicknesses of the box body and/or ribs, material, or the like.
Furthermore, it is more preferable that each of the transferring members is divergent such that a basic sectional area increases toward each of the impact absorbing members. By employing such a construction, the basic sectional area on the side for absorbing and receiving the load is larger than that on the load input side, thereby stabilizing the member. Therefore, when the impact is transferred to the connecting portion, the load transferring member does not tilt or rotate in the vertical direction and the dispersed impact load can be reliably transferred to the impact absorbing member.